An Offshore Buoy as a Fad in the Mediterranean

The role of a large offshore buoy in attracting and maintaining fish assemblages was investigated. The ODAS (Oceanographic Data Acquisition System) 1 buoy was a 42 m long vertical cylinder, 80 cm in diameter, with a stabilizing disk at its tip. The buoy remained 4 years in the Ligurian Sea from winter 1987 onward, moored by chains to the bottom at 1,100 m, 30 miles off the coast. Twenty underwater observations carried out in different seasons at depths of 0–40 m showed the presence of at least 10 fish species (Naucrates ductor, Seriola dumerili, Polyprion americanus, Thunnus thynnus, Trachurus sp., Balistes carolinensis, Schedophilus ovalis, Centrolophus niger, Parablennius spp.) with a maximum presence during summer. Numerical censuses, sizes and behavioral notes about the associated fish are presented. More detailed observations on Naucrates ductor (length/frequency distributions, sex ratio, feeding behavior) are given.